1. Field of the Invention
The present invention relates to the field of conveyors in general, and in particular to a power-driven conveyor with an endless belt driven by a pneumatic cylinder and a pawl mechanism.
2. Description of the Prior Art
A variety of different types of power-driven or live conveyors have heretofore been developed. Such conveyors include driven members and drive mechanisms. For example, the driven members include rollers, chains and belts. Drive mechanisms for live conveyors include various kinds of motors operably connected to the driven members.
In operation, power-driven or live conveyors may run continuously or, alternatively, their driven members may move incrementally in response to commands from a control system. Such incremental driven member movements in the latter type of power-driven conveyor may be accomplished by means of, for example, stepper motors.
Stepper motors rotate in short and substantially uniform angular movements or steps. Typical steps comprise thirty degrees, forty-five degrees and ninety degrees of rotation. The driven member of a conveyor and such a motor moves in corresponding increments when the stepper motor is actuated by the conveyor control system.
However, precise positioning of a driven member is difficult to achieve with a stepper motor because positioning errors tend to be cumulative. Such errors may be the result of step deviations of a few degrees plus or minus. Also, errors can be caused by slippage or wear in the driven member or the drive mechanism and by overcoat of the driven member. Unless the conveyor control system is programmed to reset the driven member and the drive mechanism with respect to each other, the positioning errors cumulate so that the relative misposition increases with each incremental movement.
Furthermore, stepper motors powerful enough for material handling conveyors are relatively expensive compared to continuously driven motors. Reset mechanisms for solving the aforementioned cumulative positioning error problem also add to the cost and complexity of conveyors with stepper motors. Their relatively high cost is particularly disadvantageous in conveyor systems, such as automatic order filling systems, wherein large numbers of individual conveyors are employed.
In automatic order filling systems, orders are filled by collecting predetermined quantities of particular articles for ultimate delivery to customers. For dispensing the goods at precise intervals according to the requirements of each customer order, stepping conveyors with incremental movements may be employed to advantage. For example, each conveyor cycle may result in a predetermined number of specific articles being dispensed into a receptacle. The orders may be filled from a number of different articles each of which is dispensed by a separate, individually controlled conveyor. Furthermore, for some articles which are frequently required in multiples, it may be desirable to provide several conveyors each dispensing a different number of the articles per cycle.
However, heretofore there has not been available a relatively inexpensive, power-driven stepping conveyor capable of consistent, uniform incremental movements and especially well suited for automatic order filling systems.